Electromagnetic braking device on continuous casting molds

ABSTRACT

To bring about a direct effect on the fluid streams exiting the mould dip tube ( 2 ) of moulds in continuous casting moulds ( 1 ) of a continuous casting plant for casting liquid metals, in particular liquid steel materials for producing slab and thin slab products with format widths of 750 to 3500 mm and format thicknesses of 30 to 500 mm, said casting plant being equipped with an electromagnetic braking device for improving the product quality, it is proposed to dispose at least two poles ( 10 ) per mould broad side ( 3 ) symmetrically with respect to the perpendicular reference line ( 4 ) of the mould dip tube ( 2 ) such that the primary axes ( 12 ) of the poles&#39; outlet cross section ( 11   a ) are aligned at a specific angle (α 1  and α 2 ) relative to the perpendicular reference line ( 4 ) of the mould dip tube ( 2 ).

The invention concerns a method and a device for casting liquid metals, especially liquid steel works materials, to produce slab and thin-slab products with format widths of 750 to 3,500 mm and format thicknesses of 30 to 500 mm in a continuous casting installation, which, for the purpose of achieving improved product quality, is equipped with an electromagnetic braking device that consists of coils with cores and a yoke, by whose generated magnetic field effect the flow conditions within the liquid metal in the mold are controlled.

To improve product quality by exerting a positive effect on the flow conditions within the continuous casting mold, it is already known that the mold can be equipped with an electromagnetic brake, which consists of coils with cores and a yoke, with which magnetic fields are generated, which are used to influence the flow conditions prevailing in the steel bath within the mold. In this connection, to develop the fullest possible effectiveness of the magnetic fields, it is necessary to bring the magnetic fields as close as possible to the continuous casting mold. Therefore, usually either the electromagnetic braking systems are moved up to the mold by hydraulic or electromechanical means only after the mold has been placed in the casting machine or they are permanently installed in various arrangements on the mold of the continuous casting installation. In this regard, basically, the coil or the coil combinations, each with a core, are positioned from the outside on the mold or on the water tank, through which water flows, or on the rear side of the copper plate, or the coil is permanently fixed on the structural steel work, and a moving core is moved through it into the mold.

WO 2004/022264 A1, for example, discloses an electromagnetic braking device for molten steel flowing into a continuous casting mold, which comprises at least one magnetic coil with a ferromagnetic core assigned to the broad sides of the mold. To reduce the oscillating masses and at the same time increase the strength of the magnetic field, the core consists, on the one hand, of a primary part that houses the magnetic coil and can be moved to vary its distance from the broad-side walls and, on the other hand, of attachments that are fixed in water tanks of the mold, such that the parts of the core, when they are move together into their operating position, form U-shaped yokes to generate a closed magnetic flux.

DE 10 2004 046 729 A1 discloses a magnetic brake for a continuous casting mold, in which a magnetic field generated by permanent magnets is meant to control the flow of the liquid metal. To obtain variation of the magnetic field strength, the permanent magnets arranged on the mold can be variously adjusted in groups to alter the field strength distribution. In this regard, provision is also made for permanent magnets to be arranged in the water tank of the continuous casting mold and for it to be possible to adjust them to rest directly against the mold plate.

DE 600 16 255 T2 describes a device for casting metals that has an electromagnetic brake comprising magnetic cores, which are permanently mounted on one side of the mold in such a way that they cover essentially the whole width of the mold except for a central section and which are connected with a removable yoke, wherein the winding is arranged around the yoke in such a way that the central axis of the winding extends essentially parallel to a longitudinal axis of the mold and at right angles to the casting direction of the mold. As a result of these measures, the originally vertically directed flow velocity of the liquid metal cast in the vicinity of the inlet tube is reversed or at least strongly reduced (braked). In addition, horizontal and vertical rotation of the molten cast occurs.

Finally, DE 602 19 062 T2 describes a device for casting metals, wherein magnetic elements comprising magnetic cores and electric conductor windings are arranged along each longitudinal side of the mold. These magnetic elements generate a magnetic field by an applied polyphase alternating voltage. This arrangement of magnetic elements makes it possible to control the movement of the molten material near the upper surface in the end regions and to brake the downward movement of the molten cast.

Proceeding from the prior art described above, the objective of the invention is to specify an arrangement and alignment for the poles of the electromagnetic braking systems by which it is possible to achieve direct control of the flow of the molten steel from the dip tube of the mold.

This objective is achieved with the characterizing features of claim 1. To achieve direct electromagnetic control of the streams of liquid emerging from the mold dip tube, at least two poles on each broad side of the mold are arranged symmetrically to the vertical reference line of the mold dip tube, such that the primary axes of the exit cross sections of the poles are suitably aligned at a certain angle a₁ and a₂.

As a result of the alignment of the poles of the electromagnetic braking device in the primary flow direction of the dip tube flow, the electromagnetic braking device directly controls, as a locally acting field, the streams of liquid emerging from the mold dip tube with respect to their direction, their velocity profile, and their turbulence structure. As a result of the liquid streams modified in this way, the development of detrimental velocity fluctuations in the bath surface are advantageously limited and can thus be controlled. The results that can be achieved in this way include low turbulence in the bath surface, fewer undesirable inclusions of, for example, casting flux or slag, and a homogeneous temperature distribution, and thus all together improved quality of the cast products and an increase in the casting rate.

Due to the concentrated effect of the design and arrangement, in accordance with the invention, of the poles of the electromagnetic braking device on the dip tube flow, the power requirement of the braking device is very low and amounts to only about ¼ to ½ of the electric power that it would otherwise be necessary to supply, and, in addition, it is not necessary to adapt the braking device as a function of the format width, but rather it is only necessary to provide for adjustment of the field strength as a function of the throughput.

In this connection, the braking device is operated basically with a permanent field and adjustable field strength by means of direct current; but operation with alternating field strength and possible reversal by means of alternating current is an alternative possibility.

The poles of the electromagnetic braking device of the invention have any desired exit cross section with the formation of a primary axis. This exit cross section can be formed, for example, as a triangle, rectangle, any desired polygon, or with a curved contour.

In accordance with the invention, the primary axes are aligned in a well-defined way, such that the primary axes of the poles intersect the vertical reference line of the mold dip tube above the poles at an angle a₁ of 1° to 89° or, alternatively, below the poles at an angle a₂ of 1° to 89°.

The angles a₁ and a₂ are manually set by rotation of the poles before operation of the continuous casting installation, or, in accordance with another embodiment of the invention, they are variably adjusted by motorized rotation of the poles during the operation of the continuous casting plant and then changed as required, where the motorized adjustment of the angles is accomplished, for example, by means of a motor, a hydraulic rotary drive, or a hydraulic or pneumatic cylinder. The possible centers of rotation of the poles preferably lie on their primary axes, but, alternatively, they can also be arranged outside the poles, depending on the geometric realization of the poles.

In one possible embodiment of the invention, the electromagnetic braking device with coils, cores and yoke is positioned directly on the mold, so that it oscillates together with the mold during the operation of the continuous casting installation.

In another possible embodiment of the invention, the electromagnetic braking device is permanently mounted separate from the mold, so that in this case it does not oscillate together with the mold.

Finally, it is also possible to divide the electromagnetic braking device into separate parts, with, for example, the ends of the poles being arranged on the mold, and the coils, the split core, and the yoke being positioned on the stationary machine structure.

Further advantages and details of the invention are more fully explained below with reference to the specific embodiments illustrated in the accompanying schematic drawings.

FIG. 1 shows a perspective view of a mold with an electromagnetic braking device.

FIG. 2 shows a cross-sectional side view of a mold for thick slabs with an electromagnetic braking device.

FIG. 3 shows a cross-sectional side view of a mold for thin slabs with an electromagnetic braking device.

FIGS. 4 and 5 show the mold of FIG. 2 with rotatable poles in different angular positions.

FIGS. 6 to 8 show the mold with rotatable poles in different angular positions with an alternative pole design.

FIG. 9 shows examples of pole designs with the primary axis indicated.

FIG. 1 shows a perspective view of the mold 1 of a continuous casting installation with an electromagnetic braking device arranged in the lower region of the mold dip tube 2. The electromagnetic braking device, which consists of the cores 14, the yokes 14′, and the magnetic coils 13, is arranged in such a way in accordance with the invention that two poles 10 are positioned opposite each other on each broad side 3 of the mold. They are aligned symmetrically to the vertical reference line 4 of the mold dip tube 2 relative to the principal flow direction of the dip tube flow, so that the primary axes 12 of the exit cross sections of the poles intersect this reference line 4 at a certain angle a₁. As a result of the reference of the alignment of the poles 10 to the principal flow direction of the dip tube flow, the streams of liquid flowing into the mold 1 are controlled in a direct way by the magnetic field lines created between the poles 10. The principal flow direction of the dip tube flow, which is not shown in the perspective view of FIG. 1, is shown in the cross-sectional side views of FIGS. 2 to 5.

FIG. 2 shows a mold 1 for thick slabs with the principal flow direction 5 of the dip tube flow emerging laterally from the mold dip tube 2 at about right angles. Corresponding to this principal flow direction 5, a pole 10 is arranged on each side in the lower region of the mold dip tube 2 in such a way that the primary axes 12 of the exit cross section 11 _(a) of each pole 10 intersects the vertical reference line 4 of the mold dip tube 2 at an angle a. Since the point of intersection is located above the poles 10, this angle is denoted a₁.

FIG. 3 shows a mold 1 for thin slabs with the principal flow direction 5 of the dip tube flow emerging laterally from the mold dip tube 2 at an angle of about 45°. The arrangement of the poles 10 with respect to this principal flow direction 5 is changed from that of FIG. 2 in that the point of intersection of the primary axes 12 of the exit cross section 11 _(a) of each pole 10 with the vertical reference line 4 of the mold dip tube 2 is now located below the poles 10, and for this reason the angle of intersection is denoted a₂ to distinguish it from a₁.

FIGS. 4 and 5 show an alternative realization of an electromagnetic braking device for a thick slab mold 1 of the type illustrated in FIG. 2 for adaptation to altered conditions of the streams of liquid emerging from the mold dip tube 2. The poles 10 of this embodiment are designed to rotate clockwise 18 or counterclockwise 19 about a point of rotation 20 that lies on the primary axes 12 of the exit cross section 11 _(a). In FIG. 5, the two poles 10 were rotated clockwise 18 or counterclockwise 19 from their original positions in FIG. 4. This caused the original angle a₁ in FIGS. 2 and 4 to increase to a new value a₁′ in FIG. 5.

FIGS. 6 to 8 show examples of possible rotations of the poles 10. The poles 10, which are formed with a curved contour of their exit cross sections 11 _(e), are arranged symmetrically to the vertical reference line 4 of the mold dip tube 2 in the region of the outlet 6 of the mold dip tube 2. FIG. 6 shows an assumed initial position. The initial position of the poles 10 shown in FIG. 6 was changed to the position shown in FIG. 7 by rotating the left pole 10 inward in direction of rotation 18, i.e., clockwise, and rotating the right pole 10 inward in the opposite direction of rotation 19 by an angular amount of 5° in each case. Rotation of the poles 10 outward in the opposite directions by an angular amount of 20° changes the positions of the poles 10 from their initial positions shown in FIG. 6 to the new positions shown in FIG. 8.

To show exit cross sections 11 of the poles 10 that can be used in accordance with the invention, FIG. 9 shows a selection of various possible exit cross sections 11. The exit cross sections 11 are shown with the primary axis 12 of the exit cross section 11 indicated. The upper row of drawings shows assumed initial positions, and the lower row shows the end positions obtained by rotation in direction of rotation 19 by a certain angular amount. In detail, the following exit cross sections are shown from left to right:

-   -   rectangular exit cross section 11 _(a),     -   triangular exit cross section 11 _(b),     -   polygonal exit cross section 11 _(c), and     -   oval exit cross section 11 _(d).

LIST OF REFERENCE NUMBERS AND LETTERS

-   1 mold -   2 mold dip tube -   3 mold broad side -   4 vertical reference line of the mold dip tube -   5 principal flow direction of the dip tube flow -   6 outlet of the mold dip tube -   10 pole -   11 _(a-e) exit cross section of the pole -   12 primary axis of the exit cross section of the poles -   13 magnetic coils -   14 core -   14′ yoke -   15 magnetic field lines -   16 point of intersection above the poles -   17 point of intersection below the poles -   18 direction of rotation (clockwise) -   19 direction of rotation (counterclockwise) -   20 point of rotation -   a₁ angle between the vertical reference line of the mold dip tube     and the primary axis in the exit cross section of the poles with the     intersection located above the poles -   a₂ angle between the vertical reference line of the mold dip tube     and the primary axis in the exit cross section of the poles with the     intersection located below the poles 

1-17. (canceled)
 18. A method for casting liquid metals to produce slab and thin-slab products with format widths of 750 to 3,500 mm and format thicknesses of 30 to 500 mm in a continuous casting installation, which is equipped with an electromagnetic braking device that includes coils with cores and a yoke, comprising the steps of: controlling flow conditions within the liquid metal in a mold with a magnetic field effect generated by the electromagnetic braking device; and achieving direct electromagnetic control of streams of liquid emerging from a mold dip tube by arranging at least two poles opposite each other with mirror symmetry on each broad side of the mold and by arranging at least two poles symmetrically to a vertical reference line of the mold dip tube on each broad side of the mold, so that primary axes of exit cross sections of the poles are aligned at an angle a₁ or a₂ of 1° to 89° to a principal flow direction of the dip tube flow.
 19. The method in accordance with claim 18, including aligning the primary axes in a well-defined manner so that the primary axes of the poles intersect the vertical reference line of the mold dip tube above the poles at an angle (a₁) of 1° to 89° or, alternatively, below the poles at an angle (a₂) of 1° to 89°.
 20. The method in accordance with claim 19, including manually setting the angles (a₁, a₂) by rotating the poles before operation of the continuous casting installation.
 21. The method in accordance with claim 19, including variably adjusting and changing the angles (a₁ and a₂) by manual or motorized rotation of the poles during operation of the continuous casting plant, as required.
 22. The method in accordance with claim 18, including adjusting field strength of the braking device as a function of throughput of the mold.
 23. The method in accordance with claim 18, including operating the braking device with a permanent field and adjustable field strength by direct current.
 24. The method in accordance with claim 18, including operating the braking device with alternating field strength and possible reversal by alternating current.
 25. A mold of a continuous casting installation for casting liquid metals to produce slab and thin-slab products with format widths of 750 to 3,500 mm and format thicknesses of 30 to 500 mm, comprising an electromagnetic braking device that includes coils with cores and a yoke, the braking device being operative to generate a magnetic field effect to control flow conditions within liquid metal in the mold, wherein at least two poles are arranged opposite each other with mirror symmetry on each broad side of the mold, and at least two poles are arranged symmetrically to a vertical reference line of a mold dip tube on each broad side of the mold so that a direction of primary axes of exit cross sections of the poles substantially corresponds to principal flow directions of the dip tube flow, and wherein the primary axes intersect the vertical reference line of the mold dip tube above the poles at an angle (a₁) of 1° to 89° or, alternatively, below the poles at an angle (a₂) of 1° to 89°.
 26. The mold in accordance with claim 25, wherein the poles have various exit cross sections which are formed with a primary axis.
 27. The mold in accordance with claim 26, wherein the poles have various exit cross sections selected from the group consisting of: a triangle, rectangle, any desired polygon, or with a curved contour.
 28. The mold in accordance with claim 25, wherein the poles are aligned in a stationary geometric arrangement on the mold at the angle (a₁, a₂) to the vertical reference line of the mold dip tube.
 29. The mold in accordance with claim 25, wherein the poles are rotatable for manual or motorized adjustment of the angle (a₁ or a₂) before or during operation of the continuous casting installation.
 30. The mold in accordance with claim 29, and further comprising a motor, a hydraulic rotary drive, a hydraulic cylinder or a pneumatic cylinder for motorized adjustment of the angles.
 31. The mold in accordance with claim 29, wherein a center of rotation of the pole lies on the primary axis of the pole.
 32. The mold in accordance with claim 29, wherein a center of rotation of the pole lies outside the pole.
 33. The mold in accordance with claim 25, wherein the electromagnetic braking device with the magnetic coils, the cores and the yoke is positioned directly on the mold and oscillates together with the mold during operation of the continuous casting installation.
 34. The mold in accordance with claim 25, wherein the electromagnetic braking device is permanently mounted separate from the mold and does not oscillate together with the mold.
 35. The mold in accordance with claim 25, wherein the electromagnetic braking device is divided into separate parts so that ends of the poles are arranged on the mold, and the magnetic coils, the core, and the yoke are positioned on a stationary machine structure. 